This invention relates to a twist-lock pin and tapered drill for improving the retention and resistance characteristics of plastic dental restorative materials and, more particularly, the invention is concerned with providing a tapered left-hand threaded pin for insertion into a hole in a tooth drilled with a geometrically similar drill bit. Slight rotation of the pin in a counter-clockwise direction causes the threads to bite simultaneously, effectively locking the pin into place.
Heretofore, it has been the common practice to anchor a superstructure to the understructure of a tooth by drilling one or more holes into the tooth or understructure. A pin or rod is inserted in each of the holes and allowed to extend above the understructure so that the exposed portion of the pin may be used to anchor the superstructure onto the tooth. The pins are relatively small in diameter and difficult to handle. It is especially difficult to insert the pin in the hole where the hole is undersized and the pin is threaded. An example of a prior art device is described in U.S. Pat. No. 3,434,209 and is manufactured and distributed by Whaledent International of New York, N.Y. In this prior art device called the T.M.S. system, the pin requires ten complete revolutions to seat a distance of 2 mm. Also, the tool for inserting the T.M.S. pin is a slotted screwdriver design which does not hold the pin securely causing problems during initial pin insertion. This can lead to unwanted pin shear and uneven stress loading of the tooth structure if the pin is not in exact alignment in the hole.
What is needed is a dental anchor pin which can be easily inserted into the opening in the tooth with a minimum of rotation being required. The pin should be easier to align in the tooth opening with position control of the pin during insertion. Also, the rate of loading of the pin should be more rapid than presently available pins in order to provide the operator with greater "feel" and ability to forecast and prevent ultimate torsion failure.
The hereinafter described twist-lock pin and drill disclose a system which will provide all of the desired features noted above. The pin is easier to insert since the tip of the pin is smaller than the surface diameter of the pinhole in the tooth. The pin seats in a counter-clockwise rotation and less than 360.degree. rotation is required to fully seat the pin in the tooth opening. Also, because of the counter-clockwise rotation of the pin, the action of the cut-off bur which rotates clockwise, serves to seat the pin deeper and more securely in the tooth rather than loosen it when the excess portion of the pin is reduced.